1. Field of the Invention
The present invention relates to a lock control system, a lock controller, and a key device, more particularly to a system in which a plurality of key devices, used individually or in combination, control the opening and closing of a lock.
2. Description of the Related Art
Doors are customarily locked and unlocked by the use of a key. The traditional method of locking or unlocking a door is to insert the key into a keyhole by hand and then turn or press the key. A problem with this method is that it is difficult for a person who is manually or visually impaired. This problem particularly affects senior citizens, whose hand and arm functions and vision tend to deteriorate with advancing age. In today's aging society, this is a problem that needs to be solved.
One proposed solution is a lock operation system in which the entrance door to a dwelling is locked and unlocked by a lock controller that receives a signal from a wireless key device. A description can be found in, for example, Japanese Unexamined Patent Application Publication No. 2001-132293. When a user of this proposed system presses a button on the wireless key device, the device sends an identifying signal to the lock controller. When the lock controller receives this signal, it decides whether the signal was sent by a device authorized to operate the lock. If it was, the lock controller changes the lock either from the locked state to the unlocked state or from the unlocked state to the locked state. A user of this system can easily lock or unlock the door without having to insert a conventional key, and by pressing the button at a distance from a plurality of similar doors, thus the user can easily find the door which the key device can unlock.
This system can be modified so that the lock is operated by a plurality of wireless key devices, each transmitting a different identifying signal. For maximum security, the system can be designed so that all of the wireless key devices are necessary to operate the lock. Alternatively, the lock can be made to respond to signals transmitted from, for example, an arbitrary majority of the wireless key devices, so that even if some of the key devices are lost, the lock can still be operated, provided that not too many of the key devices are lost. The system may also be adapted so that any one of the wireless key devices can operate the lock.
This plural-key system becomes more flexible if different weights can be assigned to the different wireless key devices. For example, if key devices that can be easily lost or misplaced are given relatively small weights, the lock can still be operated even if all of these key devices are lost, provided enough of the other key devices remain. There are, however, two problems with such a weighting scheme.
The first problem is one of convenience and practicality. Assigning weights to the key devices is a troublesome procedure for the user, and it is moreover a procedure that has to be repeated, for all key devices, whenever the number of key devices is increased.
The second problem is that when the user assigns weights, the weights are assigned subjectively, with no guarantee that the assigned weights are appropriate. Frequently, a key device which the user thinks will never be lost, does in fact become lost. Thus, it is possible that the user may assign an inadvisably large weight to an easily losable key device.